Solid nitrocellulose-nitroglycerin propellant with burning rate modifiers containing dinitroacetonitrile salts



7 June 17, 1969 Filed Jan. 16, 1963 FIG.

FIG.

N 01am BURNING RATE -IN./SEC. A 0" L. CHAILLE ETAL SOLID NITROCELLULOSE-NITROGLYCERIN PROPELLANT WITH BURNING RATE MODIFIERS CONTAINING DINITROACETONITRILE SALTS I |ll||| MATRIX COMPOSITION INGREDIENT NITROCELLULOSE (I3.I5%NI 58.5 NITROGLYCERIN 40.3 ETHYL CENTRALITE I2 MATRIX IO% DINITRO- ACETONITRILE SALT MATRIX v I l l l 7 L000 2 3 4 5 7 10,000 2 v PRESSURE -PSI EFFECT OF DINITROACETONITRILE POTASSIUM SALT ON THE BURNING RATE OF A HIGH HEAT OF EXPLOSION COMPOSITION POTASSIUM 6 12 I8 24 3O POTASSIUM DINITROACETONITRILE-WEIGHT PERCENT EFFECT OF POTASSIUM THE BURNING RATE OF A CATALYZED HIGH HEAT OF EXPLOSION COMPOSITION Sheet DINITROACETONITRILE CONCENTRATION ON IN V EN TOR S.

June 17,

SOLID NITI'IDOIIL'LIILOSE-NITRDOLYOERIN PROPELLANT WITH BURNING RATE MODIFIERS CONTAINING 1969 L ACHMLLE ET AL 3,450,583

. DINITROACETONITRILE SALTS Filed Jan. 16, 1963 Sheet, Z of 2 MATFIIx'cOIIn'POsITION 'wEIOI-I'T NITROCELLULOSE (13.15%N) 58.5 NITROGLYCERIN 401a ETHYL CENTRALITE (.2 8 5- LEADoxIDE (ADDED) 2.0 4 CARBON BLACK (ADDED) 2.3 I .z

if E

I ("LL/I g LLIIIII I l l IIIIII .1 i 5 7 1,000 2 3 4 5 7 10,000 2 PRESSURE-PSI 1 EFFECT OF POTASSIUM DINITROACETONITRILE ON THE BURNING RATE OF A CATALYZED HIGH HEAT OF EXPLOSION COMPOSITION l I I l l I l I l l 20 COMPOSITION 2Y1 INGREDIENT WEIGHT NITROCELLULOSE (13.15%N) 59.5 '3 NITROGLYCERIN 40.3 MATRIX-M7 10 -ETHYL CENTRALITE 1.2 LEAD OxIDE (ADDED) 2.0 g CARBON BLACK (ADDED) 2.3 5 I 7.0 SODIUM DINITRO- E ACETONITRILE (ADDED) (0.0 g 5.0-

4.0 o g 1 g 3 0 D m 2.0

l I l I l 1 l I l IAL I l I 7 1,000 2 3 4 5 7 10,000 2 PRESSURE-PSI FIG. 2 BURNING RATE OF A CATALYZED DOUBLE BASE PROPELLANT CONTAINING 10% SODIUM DINITROACETONITRILE JAMES L. CHAILLE ROBERT W. WALKER,

INVENTORS.

United States Patent Army Filed Jan. 16, 1963, Ser. No. 251,989 Int. Cl. C06b /00 US. Cl. 149-18 8 Claims This invention relates to a method of altering the burning rate of double-base propellants or explosive compositions. More particularly, this invention concerns a method of accelerating the burning rate of double-base propellants or explosive compositions. More specifically, this invention concerns a method of accelerating the burning rate of double-base solid propellant compositions.

It is sometimes highly desirable to accelerate the burning rate of a solid double-base propellant or explosive composition to meet the requirements for a specific use. For example, in rocket units employed to assist aircraft take-off, fast burning rates are desirable in order that suflicient thrust for take-off is quickly developed. In small shoulder fired military rockets, the total time for burning the propellant may be 20 milliseconds. Thus, to achieve a high velocity, rapid burning of the propellant is required. Similarly, when a double-base explosive composi tion is used as an igniter for other material it is imperative that this igniter burn as rapidly as possible to eliminate ignition relays.

It has now been determined that the burning rate of double-base explosive or propellant compositions can be increased by a factor of up to four or slightly higher by adding to these compositions from 4% to 40% by weight of a compound selected from the groups consisting of sodium dinitroacetonitrile and potassium dinitroacetonitrile. This increase in burning rate is gained without any apparent change in the thermal or mechanical stability and without afi'ecting the heat of explosion of the basic double-base propellant. Moreover, the temperature coefficient of the composition containing sodium dinitroacetonitrile or potassium dinitroacetonitrile is less than that of the composition without this additive. This difference is substantial in many instances. For example, potassium dinitroacetonitrile reduces the temperature coefficient to almost zero, roughly about 5% to 10% of the coeificient for the composition without the potassium dinitroacetonitrile.

In accordance with the foregoing, it is an object of this invention to provide double-base compositions having very fast burning rates.

It is a further object of the invention to provide doublebase compositions which contain potassium or sodium dinitroacetonitrile and which have very fast burning rates while still maintaining the stability and other characteristics of the parent double-base composition.

Another and still further object of the invention is to provide a method for accelerating the burning rate of double-base propellants by adding to the composition before gelling from 4% to 40% by weight of a compound selected from the group consisting of sodium dinitroacetonitrile and potassium dinitroacetonitrile.

The manner in which these and other objects may be accomplished will become apparent from the following detailed description and the accompanying drawings, in which:

FIGURE 1 is a graph showing the accelerating eifect of potassium dinitroacetonitrile in a double-base composition;

FIGURE 2 graphically illustrates the accelerating effect sodium dinitroacetonitrile has on the burning rate of a double-base composition;

FIGURE 3 is a graph depicting the accelerating eifect of potassium dinitroacetonitrile on a composition different from that of FIGURE 1; and

FIGURE 4 graphically illustrates the effect various amounts of potassium dinitroacetonitrile have on the burning rate at various pressures using the same composition as shown in FIGURE 1.

The burning rate of any double-base composition, that is, composition based on nitroglycerin and nitrocellulose plus conventional additives, can be accelerated according to the method of this invention by adding to the composition from 4% to 40% by weight potassium dinitroacetonitrile or sodium dinitroacetonitrile. As clearly evidenced by FIGURES 1 through 4, the amount of acceleration is directly related to the amount of dinitroacetonitrile added to the double-base composition if the pressure and temperature of the composition at the time of ignition remain constant. It is, of course, well known that the burning rate of any solid propellant is a function of the temperature of the propellant at the time of ignition and the pressure surrounding the propellant during combustion.

Double-base compositions and their methods of manufacture have been known in the art for many years. While the possible variations in such compositions are almost limitless, they all contain as essential ingredients from 40% to by weight nitrocellulose, 10% to 35% by weight nitroglycerin, and from 1.2% to 30% by weight of one to five various additives such as carbon black, graphite, potassium sulfate, dimethyl phthalate, and lead salts. One means of preparing double-base compositions is by the solvent process of extrusion. In this method water in hydrated nitrocellulose is removed with ethanol. The ethanol is used alone or in admixture with the colloiding solvent such as ether or acetone. If the colloiding solvent is not added with the ethanol, it is added after the ethanol treatment. The nitroglycerin and other additives such as carbon black, lead oxide, ethyl Centralite, and potassium dinitroacetonitrile are then added and a doughy mass is formed in a mixer, for example the Sigma blade mixer. The dough is then extruded into grains and cut in the desired length. The grains are dried by passing warm air over the grains. This grain can be used as such or inhibited by coating the outer surface of the grain with any of the conventional inhibitors for double-base propellant grains, such as cellulose acetate, polyvinyl alcohols, and polyvinyl acetates. The inhibitors may be applied by wrapping, dipping, spraying or painting. The smaller grains are usually inhibited by spraying or painting the outer surfaces of the grain or by dipping the grain in the inhibitor solution. Large grains are normally inhibited by wrapping the grain with an inhibiting materal.

It is to be understood that the compositions of the invention can also be prepared by other conventional methods such as casting.

The manufacture of double-base compositions containing sodium dinitroacetonitrile or potassium dinitroacetonitrile requires no departure from the conventional methods of manufacturing and therefore needs no further discussion. The dinitroacetonitrile compound is merely mixed with other ingredients in the same manner as any other additive and processed using standard techniques.

Examples of double-base compositions which can be used in the practice of the invention are given in Table I below.

TABLE I Formulation, Weight Percent Composition Ingredient 1 2 3 4 Nitrocellulose (13.15% N) 58. 5 58. 5 5 58. 5 Nitroglycerin 40.3 31.8 2 40.3 Ethyl Centralite 1.2 1.2 1 2 griaeetim 8. 5

iaraiiit'kaddea Carbon Black (added) lndicates that the ingredient is an optional catalyst which can be added in the amount specified. Example: ln Formulation 1, 2.0 grams of lead oxide and 2.3 grams of carbon black would be added to 100 grams of the composition.

NOTE.-Al1 ingredients above dotted line represent 100% by weight of double-base composition. The ingredients listed below the dotted line function as catalyst and are optional.

TABLE II Formulation, Weight Percent Composition Ingredient 1 2 Nitrocellulose (13.15% N) 51.18 40. 54 Nitroglyeerin 35.26 27. 93 Ethyl Centralite. 1.05 0. 83 Lead Oxide... 1. 75 1.39 Carbon Black 2.01 1. 59 Sodium Dinitroacetonitrile. 8. 75 Potassium Diuitroacetonitrile 27. 72

Each of the formulations of Table II was processed and extruded in the conventional manner from a 1:1 ethanolsolvent and burned in a Crawford-Huggett strand burner. The same formulations minus the sodium or potassium dinitroacetonitrile were processed and extruded in the identical manner and also tested in the Crawford-Huggett strand burner. The results, clearly showing the accelerating effect, are given in Table III.

TABLE III Burning Rate, in./sec. (25%) 1,000 5,000 10,000 20,000 Composition Tested p.s.i. p.s.i. p.s.i. p.s.i.

Formulation 1 3.2 7.0 10. 2 19. 0 Formulation 1 1 0. 7 2. 2 4. 0 7. 2 Formulation 2 1. 7 5.3 8. 5 13.6 Formulation 2 0. 7 2. 2 4. 0 7. 2

l Minus Sodium Dinitroacetonitrile. 2 Minus Potassium Dinitroacetonitrile.

The eflect on the heat of explosion exerted by either sodium or potassium dinitroacetonitrile is negligible. For example, the composition of formulation 1 has a heat explosion of 1150 cal./ g. while that of the composition minus sodium dinitroacetonitrile is 1125 cal./ g. Potassium dinitroacetonitrile also has little effect on the heat of explosion. The heat of explosion for the matrix composition of FIGURE 1 is 1125 cal./g. For the same composition, to which has been added 5%, 10%, and 20% potassium dinitroacetonitrile, the heats of explosion are 1120 cal./g., 1120 cal./g., and 1140 cal./g., respectively.

To determine the effect of the dinitroacetonitrile salts on the temperature coefficient, the high test of explosion matrix (FIGURE 2) containing 10% added sodium dinitroacetonitrile was selected for testing. The temperature coeflicient was positive from 40 C. to 25 C., but negative from 25 C. The overall coefficient (40 C. to 60 C.) has less significance since the burning rate at the upper temperature limit is not the maximum. However, the temperature coefficient of this propellant is definitely less than that of the matrix. The result of this temperature coefficient study is shown in Table IV.

TABLE IV [Burning Rates and Temperature Coelficients of Sodium Dinitroaceton trile Propellants] Temperature Coefllcient, percent 0. calculated at constant pressure from Burning Rate, in./sec.

40 C. 25 C. 60 C.

Additional tests using increased amounts of potassium and sodium dinitroacetonitrile show that the temperature coefficient is dependent upon the concentration of the dinitroacetonitrile salt, that is, the higher the concentration the lower the temperature coefficient. For instance, formulation 1 of Table II has a temperature coefficient of almost zero, being roughly 5% to 10% of that of the matrix alone. A low temperature coefficient permits the design of the rocket motor for operation in an unusually low range of service pressure in a wide temperature range.

The dinitroacetonitrile salts are elfective as burning rate accelerators for low heat of explosion double-base compositions, medium heat of explosion double-base compositions, as well as the catalyzed high heat of explosion double-base compositions generally referred to herein. This is clearly evidenced by Table V below.

TABLE V [The Eilect of Sodium Dinitroacetonitrile on the Burning Rates (in/sec. at 25 C.) of Double-B ase Compositions] Low Heat Medium Heat High Heat of Explosion of Explosion of Explosion 10% Sodium 10% Sodium 10% Sodium lrcssuro, p.s.i. Matrix Salt Added Matrix Salt Added Matrix Salt Added 0. 38 0. 8 0. 43 0. 9 0. 7 3. 0 0. 72 4. 4 1. 20 4. 0 2. 2 7. 5 1. 40 6. 0 2. 30 10. 0 4. 0 l2. 0 2. 0. 2 4. 40 17. 0 7. 2 19. 0 700 700 950 965 1, 1,

TABLE VI [Effect of Particle Size of Potassium Dinitroacetonitrile on a High Heat of Explosion Double-Base Composition] Burning Rate, in./sec.

Particle Size 1,000 p.s.i. 5,000 p.s.i. 10,000 p.s.i. 20,000 p.s.i.

From Table VI, it can be seen that up to particles of 125 micron size, increasing the particle size generally increases the burning rate. Above the 125 micron size particles, the burning rate tends to be only slightly affected by the particle size of the dinitroacetonitrile salt.

The compositions containing the sodium and potassium salts of dinitroacetonitrile, especially the sodium salt, are sensitive to humidity and should be stored in dry locations. A double-base composition containing sodium dinitroacetonitrile stored at ambient humidity exhibited a burn ing rate intermediate between that of the composition immediately after processing and that of the matrix. Drying at 60 C. restored the burning rate of the composition to what it had been immediately after processing. This is consistent with the fact that the hydrate of sodium dinitroacetonitrile reverts to the anhydrous form at 60 C.

Due to the usual similarity between sodium and potassium salts, it was totally unexpected that sodium dinitroacetonitrile caused a much larger acceleration of burning rates than did potassium dinitroacetonitrile when the compositions were tested in the Crawford-Huggett strand burner. FIGURES 1 and 2 graphically illustrate the difference. Based on the same matrix, the burning rate achieved by a 10% addition of potassium dinitroacetonitrile at 10,000 p.s.i. is between 4 inches and 5 inches per second while the addition of 10% sodium dinitroacetonitrile gives a burning rate of over 11 inches per second at the same pressure.

To determine the cause of this unique effect of the sodium salt, an extensive study was made of the physical and chemical properties of both the sodium and potassium salt. It was found that the only significant dilference between the two was the tremendously greater solubility of the sodium salt in polar solvents. This difference is shown in Table VII below.

Through the use of photomicrography and additional testing, it was shown that the unusual increase in the rate of burning resulting from the use of the sodium salt is related to its solubility. Photomicrographs of cross sections of strands containing sodium or potassium dinitroacetonitrile (the compositions of FIGURES l and 2, 10% addition of salt) show good dispersion of the salts in the strands. Longitudinal sections of strands containing potassium dinitroacetonitrile also show good dispersion in the photomicrographs. However, longitudinal sections of the strands containing sodium dinitroacetonitrile showed definite crystal aggregation clearly oriented in the direction of extrusion. These elongated crystal aggregations were well dispersed along the entire length of the strand and were found consistently in all strands examined.

To demonstrate that the solubility of sodium dinitroacetonitrile is responsible for crystal aggregation, an identical composition (same as composition of FIGURE 2, 10% addition of salt)was made using a 2:1 ether-ethanol mixture as the solvent (sodium dinitroacetonitrile solubility, 11 g./ g.) instead of the usual 1:1 acetoneethanol mixture (sodium dinitroacetonitrile solubility, 50 g./ 100 g.). Photornicrogra-phs of longitudinal and cross sections showed even dispersion of the salt throughout. Strand burning rates measured in the Crawford-Huggett strand burner were approximately the same as that of the composition having 10% potassium dinitroacetonitrile added as shown in FIGURE 1. This was the expected result since the potassium and sodium salt should give approximately the same rate of acceleration if their dispersion is the compositions being tested is substantially the same.

Moreover, these same strands containing sodium dinitroacetonitrile which burn so rapidly in the strand burner, burn at approximately the same rate as the corresponding potassium dinitroacetonitrile containing compositions when burned in a vented vessel. This is due to the fact that burning in the strand burner is parallel to the direction of extrusion and thus in line with the elongated crystal aggregation of sodium dinitroacetonitrile while burning in a vented vessel is perpendicular to the direction of extrusion and thus not in the direction of crystal aggregation.

From the discussion and graphs presented hereinabove, it can be seen that the addition of sodium or potassium dinitroacetonitrile to double-base compositions can greatly accelerate the burning of the composition. The amount of acceleration is dependent upon the quantity of potassium or sodium dinitroacetonitrile added. The addition of 10% of either salt gives approximately a 60% increases in burning rate regardless of the method of processing. However, the addition of sodium dinitroacetonitrile to composition can increase the burning rate by 300% to 400% if the composition is extruded in small strands or grains from a polar solvent which is a good solvent for sodium dinitroacetonitrile and if the strands are inhibited or otherwise treated to cause combustion to progress along a line parallel to the direction of extrusion.

Other salts of dinitroacetonitrile such as guanidinium dinitroacetonitrile, ammonium dinitroacetonitrile, cesium dinitroacetonitrile, and lead dinitroacetonitrile have been tested and found not as desirable as the potassium and sodium salts for various reasons such as poor stability and low accelerating elfect on burning rates.

The alkali metal salts of dinitroacetonitrile are old in the art. The salts correspond to the following formulae:

Generally the method of preparing these derivatives has been to reduce trinitroacetonitrile, C(NO' CN with hydrogen bromide to give the acid form, HC(NO CN. The acid form is unstable and reacts with potassium hydroxide or sodium hydroxide to yield the corresponding salt. An advantageous modification in this synthesis is mixing trinitroacetonitrile with ethanol and aqueous potassium or sodium bromide solution at 35 to 60. Usually 250 ml. to 1,000 ml. of water are used per gram mole of the alkali metal bromide and ml. to 2,500 m]. of ethanol is used per gram mole of trinitroacetonitrile.

An example of the preparation of the potassium salt is as follows:

To 700 ml. of 95% ethyl alcohol was added 238 grams of potassium bromide in 550 ml. of water. This mixture was placed in a reaction vessel equipped with a watercooled reflux condenser, thermometer, stirrer, and a bath for cooling or heating. To the contents of the vessel was added over a four minute period 176 grams of trinitroacetonitrile in 369 ml. of carbon tetrachloride. The temperature varied between 35 C. to 48 C. during the addition and precipitation began almost immediately. By external cooling (ice bath) the temperature was held between 40 C. and 57 C. for an hour during which time there was some refluxing of carbon tetrachloride and water. The reactions mixture was cooled to C. and filtered. The filter cake was washed with 100 ml. of ethanol and dried under slightly reduced pressure. The filter cake consisted of 147 grams of potassium dinitroacetonitrile and 13 grams of potassium bromide. The bromide is easily extracted with water to give an essentially pure product.

Substituting sodium bromide for potassium bromide in the above example gives the sodium salt.

The incorporation of potassium dinitroacetonitrile into a double base propellant composition can be accomplished merely by mixing the ingredients of the composition together in the conventional manner of preparing double base compositions. For example, the composition shown in FIGURE 1 having 5% by weight potassium dinitroacetonitrile added thereto is prepared according to the procedure given below.

To a mixture of 234 grams of nitrocellulose, 161.2 grams of nitroglycerin, 4.8 grams of ethyl Centralite, 8 grams of lead oxide, 9.2 grams of carbon black, and 20 grams of potassium dinitroacetontrile there is added sulficient 1:1 ethanol-acetone mixture to yield a thick doughy mass after thoroughly mixing in a mechanical mixer. The doughy mass is then extruded into grains in a conventional extrusion press. The grains are cut into desired lengths and allowed to dry. Drying is expedited by passing warm air at a temperature of 70 C. to 75 C. over the grains since the acetone and ethanol are readily volatilized at higher temperatures.

No undue limitation is to be imposed upon the scope of the invention from the above detailed discussion except as appears in the appended claims.

We claim:

1. A double base propellant composition consisting essentially of 40% to 85% by weight nitrocellulose, 10% to 35% by weight nitroglycerin, and from 1.2% to 30% by weight collectively of one to five additives selected from the group consisting of carbon black, graphite, potassium sulfate, dimethyl phthalate, ethyl Centralite, triacetin, dinitrotoluene, and lead oxide, said composition having added thereto as a burning rate modified from 4% to 40% by weight based on the total weight of said composition a member selected from the group consisting of sodium dinitroacetonitrile and potassium dinitroacetonitrile.

2. A double-base solid propellant composition consisting essentially of 51.18% nitrocellulose, 35.26% nitro- 8 glycerin, 1.05% ethyl Centralite, 1.75% lead oxide, 2.01% carbon black, and 8.75% sodium dinitroacetonitrile, said percentages referring to percent by weight of the composition.

3. A double-base solid propellant composition consisting essentially of 40.54% nitrocellulose, 27.93% nitroglycerin, .83% ethyl Centralite, 1.39% lead oxide, 1.59% carbon black, and 27.72% potassium dinitroacetonitrile, said percentages referring to percent of weight of the composition.

4. The method of accelerating the burning rate of a solid base propellant composition, said composition consisting essentially of 40% to by weight nitrocellulose, 10% to 35% by weight nitroglycerin, and from 1.2% to 30% by weight collectively of one to five additives selected from the group consisting of carbon black, graphite, potassium sulfate, dimethyl phthalate, ethyl Centralite, triacetin, dinitrotoluene, and lead oxide, said method comprising the addition to said composition of 4% to 40% by weight of a member selected from the group consisting of sodium dinitroacetonitrile and potassium dinitroacetonitrile based on the total weight of said composition.

5. The method of accelerating the burning rate of strands of a solid double-base propellant composition, said composition consisting essentially of 40% to 85 by weight nitrocellulose, 10% to 35% by weight nitroglycerin, and from 1.2% to 30% by Weight collectively of one to five additives, said additives being members selected from the group consisting of carbon black, graphite, potassium sulfate, dimethyl phthalate, ethyl Centralite, triacetin, dinitrotoluene, and lead oxide, said composition having added thereto sodium dinitroacetonitrile in an amount of 4% to 40% by weight based on the total weight of said composition, said strands having been extruded from a solvent mixture in which sodium dinit-rotracetonitrile is very soluble, said method comprising inhibiting the strands so that upon ignition, combustion progresses parallel to the direction of extrusion.

6. The method according to claim 5 wherein said solvent mixture is ethyl acetate-acetone mixtures.

7. The method according to claim 5 wherein said solvent mixture is an ethanol-acetone mixture.

8. The method according to claim 7 wherein said solvent mixture is a 1:1 ethanol-acetone mixture.

No references cited.

BENJAMIN R. PADGETT, Primary Examiner.

US. Cl. X.R. 

1. A DOUBLE BASE PROPELLANT COMPOSITION CONSISTING ESSENTIALLY OF 40% TO 85% BY WEIGHT NITROCELLULOE, 10% TO 35% BY WEIGHT NITROGLYCERIN, AND FROM 1.2% TO 30% BY WEIGHT COLLECTIVELY OF ONE TO FIVE ADDITIVES SELECTED FROM THE GROUP CONSISTING OF CARBON BLACK, GRAPHITE, POTASSIUM SULFATE, DIMETHYL PHTHALATE, ETHYL CENTRALITE, TRIACETIN, DINITROTOLUENE, AND LEAD OXIDE, SAID COMPOSITION HAVING ADDED THERETO AS A BURNING RATE MODIFIED FROM 4% TO 40% BY WEIGHT BASED ON THE TOTAL WEIGHT OF SAID SOMPOSITION A MEMBER SELECTED FROM THE GROUP CONSISTING OF SODIUM DINITROACETONITRILE AND POTASSIUM DINITROACETONITRILE. 